Geometry Optimisation with CASTEP

More documents

Recommendations

Info

Next: Outputs Up: Geometry Optimisation with CASTEP Previous: Electronic Minimisation Parameters Example - Bulk Silicon At this point we introduce geometry optimisation of bulk Silicon as an example. We will use the known bulk structure as a starting point and check what structure CASTEP suggests and what the bond length is optimised to. Bulk Silicon is shown in figure 1 below. Figure 1:Bulk silicon
We must now choose a supercell to enclose as few atoms as possible but still reproduce the whole structure. The following configuration can be used provided we include the relevant symmetry operations in the cell file. Figure 2:The primitive cell which we will take as our supercell The complete .cell file for this supercell is included in the link. The first thing that we notice is that we are using the abc format to specify the size and shape of the lattice. The shape of our unit cell naturally suggests that we do this. The lengths of a,b and c are the same as those in the bulk lattice. Later we will do a variable cell calculation as both an example of how to set one up and to check how accurately the primitive cell shape and contents can be optimised. Note that we are using a 2x2x2 Monkhurst-Pack grid and also the inclusion of symmetry_generate to ensure that castep is aware of the symmetry operations that our supercell satisfies. The parameters file si.param is here Notice that we can include the parameter line Comment : value This will appear in the output as a title (see the next section). Having set up our input files we can now run the job. The job is small and we will execute it on a desktop
Page 1 and 2: Next: Recipe Geometry Optimisation
Page 3 and 4: Next: Inputs Up: Geometry Optimisat
Page 5 and 6: Next: The Size and Shape Up: Inputs
Page 7 and 8: In both cases if [units] are not sp
Page 9 and 10: After the atomic symbol or the atom
Page 11 and 12: KPOINTS_MP_SPACING [units] Where is
Page 13 and 14: 2005-04-04
Page 15 and 16: Next: Atomic masses Up: The .cell f
Page 17 and 18: It is possible to fix the positions
Page 19 and 20: Next: External pressure that is Up:
Page 21 and 22: Next: General Job Parameters Up: In
Page 23 and 24: When a calculation that was stopped
Page 25 and 26: Next: Electronic Minimisation Param
Page 27 and 28: Next: Example - Bulk Silicon Up: Th
Page 29: the default value is 3 but it must
Page 33 and 34: Next: The .castep file Up: Geometry
Page 35 and 36: 4 -2.14844155E+002 -9.84322032E-003
Page 37 and 38: BFGS: Final Configuration: ========
Page 39 and 40: Next: Other output files Up: Output
Page 41 and 42: Next: A Variable Cell calculation U
Page 43 and 44: arbitrary set of basis set paramete
Page 45 and 46: 3 -2.16474423E+002 2.10512829E-007
Page 47 and 48: Figure 6:A finite vacuum gap may ca
Page 49 and 50: 0.0000000000 0.0000000000 24.503725
Page 51 and 52: thickness We can see that the total
Page 53 and 54: It is interesting to look at the ev
Page 55 and 56: Next: About this document ... Up: G

Geometry Optimisation with CASTEP

Create successful ePaper yourself

Delete template?

Save as template?